1. Field of the Invention
The present invention relates to a mobile communication apparatus and a transmission output power control circuit of the mobile communication apparatus. More particularly, the present invention relates to a mobile communication apparatus for sending out transmission outputs from a plurality of antennas and a transmission output power control circuit of the mobile communication apparatus.
2. Description of the Related Art
In a conventional technique, a high frequency output power can be varied based on the state of an antenna. A transmission output power control circuit of a mobile communication apparatus for a plurality of antennas is shown in FIG. 1.
Referring to FIG. 1, the transmission output power control circuit is composed of a variable attenuator a, a final stage amplifier b, a detecting circuit c, a switch d an antenna A e, and an antenna B f, an APC (automatic power control) processing section g, and a single reference voltage j. The variable attenuator a attenuates a high frequency input signal based on a direct current voltage inputted thereto. The final stage amplifier b amplifies an output power supplied from the variable attenuator a up to a predetermined power level. The detecting circuit c detects the power outputted from the final stage amplifier b and then converts into a direct current detection voltage by a diode m. The switch d selects one of antenna A and antenna B of a system on the basis of a signal supplied to a selection terminal. The antenna A e and antenna B f output the transmission output power of the predetermined level. The APC (automatic power control) processing section g has a single reference voltage j corresponding to the transmission output power level. The APC processing section g compares the direct current detection voltage obtained by the detecting circuit c with the reference voltage j and outputs a direct current voltage to keep the transmission output power level of constant.
Since the transmission output power control circuit has only one reference voltage j, a difference between a loss in a path from the detecting circuit c to the antenna A e and a loss in a path from the detecting circuit c to the antenna B f can not be detected. For this reason, difference of the transmission power between the antennas becomes large.
A diversity apparatus is described in Japanese Laid Open Patent Application (JP-A-Heisei 9-23176). FIG. 2 shows the circuit structure of the diversity apparatus which removes the difference of the transmission power between the antennas shown in FIG. 1.
Referring to FIG. 2, the diversity apparatus in this conventional technique is composed of a variable attenuator a', a final stage amplifier b', a switch d', detecting circuits c' and c", an antenna A e' and an antenna B f', a switch h', an APC processing section g', and reference voltages j' and k'.
The variable attenuator a' can attenuates a high frequency output power on the basis of a direct current voltage. The final stage amplifier b' amplifies the high frequency output power from the variable attenuator a' up to a predetermined power level. The switch d' selects one of antennas of an antenna A/B system on the basis of a selection signal. The detecting circuits c' and c" detect the transmission output power level in the respective antennas and then converting into the direct current voltages by diodes m' and m", respectively. The antenna A e' and antenna B f' output the transmission output powers of the predetermined levels. The switch h' selects one of the detected voltages for the antenna A e' and the antenna B f' obtained by the detecting circuits c' and c" on the basis of the selection signal. The APC processing section g' has the reference voltages j' and k' for the number of antennas (two, in FIG. 2). The APC processing section g' outputs the direct current voltage to keep the transmission output power constant. This circuit structure requires the reference voltages j' and k' and the detecting circuits c' and c" for the number of antennas.
In such a diversity apparatus, reception electric field levels are detected from signals received by the antennas A and B and an antenna indicative of the maximum reception electric field level is selected, when the antenna A e' and the antenna B f' are spaced from each other in distance. A switch signal is supplied to an antenna system A/B selection terminal and used to select one of the antennas A and B.
For example, when the antenna A e' is selected, the switch d' is set to an upper side in FIG. 2. The detection voltage obtained from the detecting circuit c' is applied to a non-inversion terminal of the APC processing section g' and then compared with the reference voltage j'. The voltage of the compared result is sent to the variable attenuator a'. Accordingly, the attenuation amount of the variable attenuator a' is adjusted such that the transmission output power from the antenna A e' is set to the predetermined level. When the transmission output power is outputted from the antenna B f', the similar operations are performed. The attenuation amount of the variable attenuator a' is adjusted in such a process on the basis of the predetermined reference voltages j' and k'. Then, the output from the variable attenuator a' is amplified by the final stage amplifier b'. Thus, the transmission output powers outputted from the antenna A e' and antenna B f' are controlled to be the predetermined levels. As a result, the difference between the antenna A and the antenna B in output power can be made small.
Also, an automatic transmission power control apparatus is described in Japanese Laid Open Patent Application (JP-A-Heisei 3-154430). In this reference, the automatic transmission power control apparatus is composed of a transmission power amplifier 4 including a variable attenuator 2 and a power amplifier 3. band pass filters 15 and 16, a transmission antenna 6, a level detector 17, an error amplifier 11 including reference voltages V1 to Vn, a differential amplifier 8, and a loop filter 10. A monitor signal component level of an output signal from the transmission power amplifier 4 is detected and converted into a detection voltage by the level detector 17. The gain of the transmission power amplifier 4 is controlled based on the detection voltage from the level detector 17.
However, the first problem of this diversity apparatus is in that the difference between the power loss from the detecting circuit c to the antenna A e and the power loss from the detecting circuit c to the antenna B e can not be detected in FIG. 1. Therefore, the difference of the transmission output between the antennas becomes large because of the difference between the transmission losses from the detecting circuit c to the antenna terminals in the conventional technique (FIG. 1).
Also, the second problem is in that the detecting circuit must be provided for each of the antennas in FIG. 2. For this reason, the circuit becomes large in size and complex as compared with the case of FIG. 1. As a result, the apparatus cannot be made small in size.